Method of treating needle blanks

Abstract: A process for tumbling needle blanks (10 or 20) either before (10) or after (20) suture holes have been drilled into the respective needle blanks (10 or 20) preferably tumbling occurs with smooth, e.g. ceramic or glass spherical media, or soft media.

Description: BACKGROUND OF INVENTION 1. Field of Invention The present invention relates to a method of mechanically treating needle blanks used for fabrication into surgical needles, and more particularly to a method for deburring and chamfering said needle blanks. 2. Background of the Art For many years, surgeons have employed needle-suture combinations in which a suture or ligature is attached to the shank end of a needle. Such needle-suture combinations are provided for a wide variety of monofilament and braided suture materials, both absorbable and nonabsorbable, e.g., catgut, silk, nylon, polyester, polypropylene, linen, cotton, and absorbable synthetic materials such as polymers and copolymers of glycolic and lactic acids. Needle-suture combinations fall into two general classes: standard needle attachment and removable or detachable needle attachment. In the case of standard needle attachment, the suture is securely attached to the needle and is not intended to be separable therefrom, except by cutting or severing the suture. Removable needle attachment, by contrast, is such that the needle is separable from the suture in response to a force exerted by the surgeon. Minimum acceptable forces required to separate a needle from a suture (for various suture sizes) are set forth in the United States Pharmacopoeia (USP). The United States Pharmacopoeia prescribes minimum individual pull-out forces as measured for five needle-suture combinations. The minimum pull-out forces for both standard and removable needle-suture attachment set forth in the United States Pharmacopoeia are hereby incorporated by reference. On typical method for securing a suture to a needle involves providing a cylindrical recess in the shank end of a needle and securing a suture therein. For example, U.S. Patent No. 1,558,037 teaches the addition of a cement material to such a substantially cylindrical recess to secure the suture therein. Additional methods for bonding a suture within a needle bore are described in U.S. Patent Nos. 2,928,395 (adhesives) and 3,394,704 (bonding agents). Alternatively, a suture may be secured within an axial bore in a needle by swaging the needle in the region of the recess. See, e.g., U.S. Patent No. 1,250,114. Additional prior art methods for securing a suture within a needle bore include expansion of a catgut suture through the application of heat (U.S. Patent No. 1,665,216), inclusion of protruding teeth within the axial bore to grasp an inserted suture (U.S. Patent No. 1,678,361) and knotting the end of the suture to be inserted within the bore to secure the suture therein (U.S. Patent No. 1,757,129). Methods for detachably securing a suture to a needle are also well known. For example, U.S. Patent Nos., 3,890,975 and 3,980,177 teach swaging a suture within a needle bore such that the suture has a pull-out value of 3 to 26 ounces. Alternative detachable attachment methods include providing a weakened suture segment (U.S. Patent No. 3,949,756), lubricant tipping the end of a suture to be inserted in the axial bore of a needle (U.S. Patent No. 3,963,031) and pretensioning a suture that is swaged within an axial needle bore (U.S. Patent No. 3,875,946) . See also, U.S. Patent Nos. 3,799,169; 3,880,167; 3,924,630; 3,926,194; 3,943,933; 3,981,307; 4,124,027; and 4,127,133. To fabricate a surgical needle, needle blanks are cut by conventional cutting means from wire stock. For those needle-suture combinations wherein the suture is inserted into a longitudinal cylindrical recess in the barrel end of the needle, one end of the needle blank is drilled by mechanical or laser means. The cutting and drilling produces burrs, and, in the case of laser drilling, burn spots which must be removed. Also, the cutting process leaves a sharp, circumferential periphery at the butt end. If the sharp edge is not removed there is a possibility that a suture connected to the needle might be cut or damaged by coming into contact with the edge. This can occur, for example, if the suture is bent sharply around in the vicinity of the needle end. Needle blanks, therefore, are subjected to mechanical treating to deburr and chamfer the needle blank. Deburring and chamfering can be accomplished by any one of several machining techniques such as grinding, lathing, and tumbling. Tumbling is a preferred method for deburring and chamfering because of its convenience. The needle blanks are placed in a drum with abrasive particles, e.g. and agitated by rotation of the drum. However, these abrasive particles, e.g., aluminum oxide, silicon oxide, zinc oxide, dull the surface. The abrasion, while deburring and chamfering the needle blank, also scratches the needle surface, thereby requiring a subsequent polishing step to renew the fine finish of the needle. Elimination of the extra polishing step would reduce the time and cost required to make a surgical needle. A further prior art method for surface treatment of needles is known from DE 2 263 500 A. This document discloses the treatment of needles with chemical and mechanical process steps. In a first chemical step, up to 0.02 mm of the needle surface is removed. A resulting oxide layer on the chemically treated surface is removed in a second mechanical step, and a third step of treatment in a centrifugal drum is needed for polishing the needle surfaces. As tumbling media for polishing, microspheres or micropins made from glass, ceramic or steel are used. SUMMARY OF THE INVENTION In the light of the known prior art, a method for tumbling needle blanks is provided herein to deburr and chamfer the needle blanks without requiring a subsequent polishing step. The method includes placing the needle blanks in a tumbler with a non-abrasive medium comprising particles having a surface smoothness sufficient to avoid scratching the needle blanks. The media may be substantially spherical. However, non-spherical media may also be employed. The media is generally smooth and softer than the blanks. The method according to the invention is defined in claim 1. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a needle blank prior to tumbling; Fig. 2 shows an end of the needle blank of Fig. 1; Fig. 3 shows a needle blank after tumbling according to the present invention; Fig. 4 shows an end of the needle blank of Fig 3; and Fig. 5 shows a typical tumbling apparatus. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The needle blanks to be treated by the tumbling operation of the present invention may be fabricated from any material suitable for the manufacture of surgical needles. Such material may be, for example, an alloy of stainless steel. The alloy is originally in the form of wire stock which is straightened (if necessary) and cut into needle blanks by processes and machinery familiar to those with skill in the art. The needle blanks typically have a diameter of from about 1.5 mils for ophthalmic needles to about 62 mils for sternum needles. A mil is one thousandth of an inch. The needle blanks may be drilled at one end, either mechanically or by laser drilling, to form an axially aligned hole therein for the reception of a surgical suture. The needle blank needs to be chamfered, deburred, ground to a sharp point and polished. Chamfering, deburring and polishing are accomplished herein by a tumbling operation wherein the needle blanks are placed in a tumbler with particles of tumbling medium. The particles of tumbling media must be able to deburr and/or chamfer the needle blanks without causing scratching of the needle surface. To accomplish this, the tumbling medium has a hardness less than that of the needle blanks (i.e. a "soft" medium). Its particles can have a smooth surface, i.e. no sharp points or edges capable of causing a visible scratch. A suitable medium may comprise particles having no curved surface feature with a radius less than the diameter of the needle blank. The media may be substantially spherical. However, non-spherical media may also be employed. The media is generally smooth and softer than the blanks. The particles of the media referred to in the claims below may be spherical and have a diameter of from about 0.5 millimeters (mm) to about 10mm, preferably about 2mm to about 7mm and a glassy smooth surface. The diameter varies with the size of the needle blank. For large (18-30 mil) wire diameters a spherical particle diameter of about 4 to about 8mm is preferred. For small (down to 10 mil) wire diameters a spherical particle diameter of about 1 to about 3mm is preferable. The present invention has the advantage that it can deburr without losing the clarity and shine of the needles. Figs. 1 and 3 show a typical needle blank end before ( blank 10) and after (blank 20) deburring, respectively. The deburring radiuses the sharp edges 15 of the needle blank end 10. This results in radiused edges 30. This helps prevent the edges from nicking and cutting a suture (not shown) during use. The media provides a burnishing surface which is free of abrasive surfaces. Thus, deburring occurs by peening rather than abrasion. The tumbling of the present invention maintains the polish of the needles. This has the major advantage of deburring without a need for repolishing the needles after deburring. Particles of soft, dry media can be of any shape suitable for tumbling. Thus, the media does not have to be spherical, e.g., wood pegs, triangles, or squares are suitable. Preferably the soft medium is formed into sperical particles. Because the soft medium is not harder than the needle blanks it will not cause scratching thereof. Examples of soft media include wood beads, ground walnut shell, e.g., Dreher NPG8 or NPG 1500 and ground corncob. Powders of silica or lime are generally added to the soft media to facilitate deburring. Tumbling with soft media is usually performed in a dry fashion. Liquid abrasives such as Dreher SFF may be added. Typically about 10ml to about 50ml of liquid abrasive are added per 2.5 liter barrel. Alternatively, 1-5 tsp./2.5 liter BBL of dry abrasives such as Dreher TPP may be added. Either centrifugal or vibratory tumbling may be employed. During centrifugal tumbling, the tumbler may be rotated about a horizontal axis. Alternatively the tumbler can agitate the needle blanks and media by means of rotation around a vertical axis. Fig. 5 schematically shows a centrifugal tumbler 40 having a drum 50. Within the drum are four chambers 60. The drum 50 turns counterclockwise while the chambers 60 turn clockwise. Such a tumbler may create up to 25 gravities of force in its chambers. The typical duration of centrifugal tumbling ranges from ten (10) minutes to one (1) hour. Additional background on centrifugal tumbling is provided by Dreher et al., Precision Sliding Grinding in Centrifugal Equipment, Industrial and Production Eng., Vol. 2 (1985), incorporated by reference. An example of a centrifugal tumbler is made by Dreher Corp., 57 George Leven Drive, Attleboro, Massachusetts 02703. This address is that of Dreher's U.S. Distributor. The parent of Dreher Corp. is a German company. Centrifugal tumbling is faster than vibratory tumbling. However, vibratory tumbling is gentler. The typical duration of vibratory tumbling is one (1) hour to sixteen (16) hours. A typical vibratory tumbler is made by Ray Tech, P.O. Box 6, Route 32, Stafford Industrial Park, Stafford Springs, Connecticut 06076 under the designations TUMBLE-VIBE and ADJUSTA-VIBE.

Claims: A process for deburring and reducing sharp edges of polished needle blanks, comprising: tumbling said polished needle blanks with media having a surface softer than the needle blanks for sufficient time to deburr said needle blanks and simultaneously retain the polish of said needle blanks. The process of Claim 1, wherein the media has a diameter from about 0.5 millimeters to about 10 millimeters. The process of Claim 2, wherein the media have a particle diameter of about 4 to about 8mm and the needle blanks have a diameter from about 18 to about 30 mils. The process of Claim 2, wherein the media have a particle diameter of about 1 to about 3mm and the needle blanks have a diameter from about 17 to about 10 mils. The process of any one of the preceding claims, wherein said media comprises wood, walnut shells or ground corn cob. The process of any one of the preceding claims, wherein said media further comprises a powder of silica or lime. The process of Claim 6, wherein the powder has a particle diameter wherein at least 98% of the particles are less than 200 mesh. The process of any one of the preceding claims, wherein an abrasive liquid is added to the media to be present during said tumbling.

Inventors: MUNOZ MARCELINO, SAMSEL SCOTT, MUNOZ, MARCELINO, SAMSEL, SCOTT
Applicants: UNITED STATES SURGICAL CORP, UNITED STATES SURGICAL CORPORATION
Application year: 1994
Main classification: B24B31
IPC codes: B24B31, A61B17, B21G1